Mc. Antle et al., Serotonin antagonists do not attenuate activity-induced phase shifts of circadian rhythms in the Syrian hamster, BRAIN RES, 813(1), 1998, pp. 139-149
A variety of observations from several rodent species suggest that a seroto
nin (5-HT) input to the suprachiasmatic nucleus (SCN) circadian pacemaker m
ay play a role in resetting or entrainment of circadian rhythms by non-phot
ic stimuli such as scheduled wheel running. If 5-HT activity within the SCN
is necessary for activity-induced phase shifting, then it should be possib
le to block or attenuate these phase shifts by reducing 5-HT release or by
blocking post-synaptic 5-HT receptors. Animals received one of four seroton
ergic drugs and were then locked in a novel wheel for 3 h during the mid-re
st phase, when novelty-induced activity produces maximal phase advance shif
ts. Drugs tested at several doses were metergoline (5-HT1/2 antagonist; i.p
.), (+)-WAY100135 (5-HT1A postsynaptic antagonist, which may also reduce 5-
HT release by an agonist effect at 5-HT1A, raphe autoreceptors; i.p.), NAN-
190 (5-HT1A postsynaptic antagonist, which also reduces 5-HT release via an
agonist effect at 5-HT1A raphe autoreceptors; i.p.) and ritanserin (5-HT2/
7 antagonist; i.p. and i.c.v.). Mean and maximal phase shifts to running in
novel wheels were not significantly affected by any drug at any dose. Thes
e results do not support a hypothesis that 5-HT release or activity at 5HT1
, 2 and 7 receptors in the SCN is necessary for the production of activity-
induced phase shifts in hamsters. (C) 1998 Published by Elsevier Science B.
V. All rights reserved.